1. Crystal structure determination

7. X-ray crystallography VS NMR are complementary techniques
NMR X-ray crystallography
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short time scale, protein folding long time scale, static structure
solution, purity single crystal, purity
< 20kD, domain any size, domain, complex
functional active site active or inactive
domains domains
atomic nuclei, chemical bonds electron density
resolution limit 2-3.5Å resolution limit 2-3.5Å
primary structure must be known primary structure must be know

23. Bragg's Law X-ray difraction W.H.Bragg 1912.
An X-ray which reflects from the surface of a substance has travelled less distance than an X-ray which reflects from a plane of atoms inside the crystal. The penetrating X-ray travels down to the internal layer, reflects, and travels back over the same distance before being back at the surface. The distance travelled depends on the separation of the layers and the angle at which the X-ray entered the material. For this wave to be in phase with the wave which reflected from the surface it needs to have travelled a whole number of wavelengths while inside the material. Bragg expressed this in an equation now known as Bragg's Law:
Bragg's Law X-ray difraction W.H.Bragg 1912.
When n is an integer (1, 2, 3 etc.) the reflected waves from different layers are perfectly in phase with each other and produce a bright point on a piece of photographic film. Otherwise the waves are not in phase, and will either be missing or feint.

24. http://www-outreach. phy. cam. ac

25. William Bragg's spectrometer The first ionization spectrometer designed and constructed by William Henry Bragg in , used to measure variations in scattering angles of crystals in order to determine their structures. This is the basis of Crystallography.
Date 1912
Place made
Leeds

26. X-ray Charcterisation
CRYSTALS program 2000
X-ray Charcterisation

27. Kappa CCD
diffractometer

28. The electron density map
crystal
colecting
X-ray
ekspozer
Difraction picture
phase
The electron density map
filtration
structural model
procesing

29. MODELING The position of these beams is related to the
What are we trying to find?
The position of these beams is related to the
periodicity of the electron density.
The intensity is related to the electron density

30. What's the first get, and FINALLY WHAT WE WANT :
lots and lots of numbers
picture
CIF file

31. Import cif
Cif file
Publish file
CIF data

32. Exchange of Results
This is usually done via text (ASCII) files. A program
is needed to convert the data into pictures and tables
• Cif files: Crystallographic Information File format.
This has become an international standard.
• SHELX files: After the name of a widely used
crystallographic program.
• PDB files: Protein Data Bank format. Often used by
modelling and graphics programs.

33. Graphics Programs-picture
There are dozens available from free viewers to
expensive modelling packages
Mercury: Free from CCDC. Has some knowledge of
symmetry operations. Reads cif files. Will output bitmap
files.
Encifer: Free from CCDC. As above, but also enables you
to read, edit and validate the syntax of cif files. Only
outputs cif files.
Ortep: Free with WINGX. A fully functional
crystallographic plotting program. Reads cif and SHELX file.

34. CHECKCIF

35. CCDC – The Cambridge Crystallographic Data Centre
CCDC maintains and distributes the CSD
(Cambridge Structural Database), plus
software for searching, viewing and analysing
crystal structures.

36. Uses of X-ray Crystallography
• Gross structure – atom types and
Connectivity
• Stereo chemistry
• Fine detail – bond lengths, angles and
torsion angles
• Electron density distributions
• Crystal Structure

37. High Quality Crystals

38. DATA COLLECTION Stages: 1. Crystal selection. Get the best you can
2. Crystal mounting. Usually oil-drop method
3. Unit cell determination. Often automatic
4. Main data collection.

39. position